Contact Region hcrwccn Two Fibres 



293 



In some sections obtained from fibers which were 

 fixed with iodium zinc chloride a swelhng elTect was 

 observed and there the detachment could have been 

 explained as being due to a compression by the glass- 

 knife during sectioning. 



A whole series of different cotton fibers and llax 

 fibers has been examined and from our observations 

 it seems that the above-mentioned detachment is 

 not due to the preparation or sectioning techniques 

 but corresponds to the actual state of the fibers 

 before examination. 



This kind of detachment described for cotton 

 fibers can be found in some rare cases also in flax 

 fibers. 



Our new fixation methods have allowed us to 

 make higher magnification micrographs. The hazy 

 dots representing isolated cellulose fibrils have made 



place for rather sharp and well-defined dots, as can 

 be seen in fig. 2. 



Fig. 3 is an example of higher magnification of a 

 longitudinal section. It confirms our idea regarding 

 the existence of a detachment of a certain number of 

 layers in the secondary wall. This detachment is 

 probably a result of the drying out of the natural 

 fibers, long before the actual examination in the 

 laboratory. 



REFERENCtS 



1. AsuNMAA, Saaka, Svt'ii.sk I'lippcisticbi. 10, 1 (1954). 



2. Castiaux, p., Raes, G., and Vandermeerssche, G., Ann. 



Textiles 2, 29 (1956). 



3. Di: MtuiEMEESTER, D., Rais, G., and Franzfn, T., Ann. 



Textiles 2,, 260 (1955). 



4. VANDFRMErRSSCHF, G. and Raes, G., Conf. Int. Teen. 



Textil. Barcelona, 1954. 



Contact Region between Two Fibres 

 Saara Asunmaa 



Paper Technology Department, Swedish Forest Products Research Laboratory, 



Stockholm 



Since new sectioning methods have been developed 

 (9, 10) the fine structure of cellulose fibres has been 

 investigated in ultrathin sections. Chemical reactions 

 and a metal impregnation have been used as contrast 

 treatments. Thallation of the fibre sample gives a 

 sufficient contrast (3, 4, 5). The reaction of thallous 

 ethylate with the fibre material furthermore only 

 applies to the accessible hydroxyl groups of the 

 cellulose fibres. In sections of fibres of holocellulose 

 of Swedish spruce (Picea excelsa), for example, a 

 parallel fibrillation was observed in the main sec- 

 ondary wall, but no parallel striation in the same 

 direction in its outermost part. The fibrils observed 

 have small dimensions, a width of down to 50 A. 

 They presumably correspond to the "fibril strings" 

 observed in hydrolyzed materials (7, 8, 11). Another 

 arrangement of similar "fibril strings" was observed 

 in different kinds of cell walls (4, 5). These "fibril 

 strings" are different from micro fibrils, which earlier 

 were observed in swollen fibres and in many other 

 botanical materials and which are several hundred A 

 wide. 



Electron micrographs of thallated fibres depict the 

 reacted thallous cellulosate and the excess reagent as 

 an impregnation medium, if present. The reactivity 

 of the fibre material under the conditions of thalla- 

 tion therefore only describes one special kind of 

 fibre reactions. 



Of particular interest from the technical point 

 of view is the fine structure of water swollen fibres. 

 Therefore a method for impregnation of fibres in 

 water-swollen state was developed (5, 6). 



The water solution of a metal compound was 

 made to penetrate the cell wall, it was reduced in 

 situ and the metal was enclosed in the fibre structure 

 by means of an effective drying. The metal content 

 observed in the micrographs demonstrates an "origi- 

 nal contrast", i.e. the contrast material is introduced 

 without chemical reactions and before the prepara- 

 tion and embedding of the material for sectioning. 

 This kind of contrast treatment is suitable for com- 

 pact materials like cellulose fibres and wood cells. 

 As a consequence of very high metal content in 

 several parts of the fibre wall, the fine structure can 

 be studied only in micrographs of the cellulose rich 

 areas with a low metal content. Such a situation is 

 observed in fibre walls of holocellulose of spruce 

 after some processing procedures, for example, after 

 a hot alkali treatment. 



Electron micrographs of hot alkalized metal- 

 impregnated fibre walls show morphological changes 

 that appeared in the holocellulose during the treat- 

 ment. Periods of broken, metal-filled canals are 

 observed both in longitudinal and in cross sections. 

 The number and shape of the metal-filled cavities in 

 the fibre section before and after the chemical treat- 

 ment show the distribution of the attacked parts 

 and probably the distribution of some reactive parts 

 in the original holocellulose fibre. The original holo- 

 cellulose fibre does not usually show similar canals, 

 or not to such an extent as the material after pro- 

 cessing. In electron micrographs at good resolution 

 a fibrillation is to be seen in the areas between the 

 metal-rich canals (5). The fibrils observed presumably 



